1. Field of the Invention
The present invention generally relates to a data and electric power transmitting/receiving apparatus used for an automatic control system, e.g., a so-called "home automation system." More specifically, the present invention is directed to a system where simultaneous data and electric power transmission and reception are carried out between a plurality of controllers and terminal devices.
2. Description of the Prior Art
Generally, the so-called "home automation (HA) system" is adapted to home electric appliances as terminal devices, and connects the terminal devices to a plurality of controllers via a common transmission line to establish data communication between the terminal devices and controllers.
Such a HA system for electronically uniting terminal devices such as air conditioners and bath heating systems is disclosed, for instance, in Japanese Patent Publication (examined application) No. 62-142431(1987). According to this conventional HA system, a control signal is transmitted from one controller via a common transmission line to the corresponding terminal device. The control signal contains an address set to one of the terminal devices. In transmitting the control signal, this controller firstly confirms that there is no control signal transmitted from others controllers or terminal devices on the common transmission line. If there are no signals on the common transmission line, this controller sends the control signal to the terminal devices through the common transmission line. Each terminal device receives the control signal only when the address contained in the control signal coincides with an address of the terminal device in question, so that the terminal devices may be controlled independently of each other. Accordingly, operations of the selected terminal devices may be readily controlled in desirable modes, such as starting and stopping operations.
In recent years, the HA systems have remarkably been enhanced as demands for conveniences have increased, and these systems have been utilized with more kinds of electric appliances. As the number of kinds of electric appliances to be controlled by the HA systems increases, it is important to quickly let an operator confirm whether or not the electric appliances are operating according to specified conditions, or whether or not the specified conditions are being maintained safely. Otherwise, the desired convenience may not be realized by the conventional HA systems.
Although the conventional HA systems can freely stop, start or leave unchanged the, operations of the terminal devices, the conventional HA systems have several drawbacks. Namely, operating conditions of one terminal device can be known by receiving a signal indicative of the operating conditions of the terminal device, after confirming that no control signal is being transmitted from the controller or that no signals indicating operating conditions of the remaining terminal devices are present on the transmission line. Therefore, a relatively longer time period is required from sending an operation instruction to one terminal device from the controller until receiving a result from the terminal device at the controller.
In controlling electric appliances by the HA systems, therefore, it is required to improve the communication speed of the HA systems.
According to another conventional HA system, a control unit is connected to various actuators and sensors through a large number of many communication lines, respectively. Therefore, the communication lines form a transmission line network for the system as a whole. Such a network formation requires difficult connection and maintenance works and tends to cause erroneous operation due to line disconnection and external noise.
An object of the present invention is to solve the drawbacks of the conventional systems and provide a data and power transmitting/receiving system to freely stop, start and release operations of selected ones of a plurality of terminal devices and improve a communication speed between a plurality of controllers and the terminal devices.
Another object of the present invention is to provide a data and power transmitting/receiving system causing no erroneous operation due to external noise and line disconnection and make connection and maintenance works easier.
Still another object of the present invention is to provide a data and power transmitting/receiving system using a two-wire communication line to almost simultaneously transmit and receive data as well as electric power between a plurality of terminal devices and controllers. Particularly, the system combines a synchronization signal with a data signal and uses the synchronization signal as electric power to the terminal devices.